1. Field of the Invention
This invention concerns the stabilization of 3-isothiazolone compounds, particularly in metal working fluid concentrates, by the incorporation with those compounds of certain sulphur-based compounds.
2. Description of the Prior Art
Isothiazolones have generated high commercial interest as microbicides to prevent spoilage of certain aqueous and non-aqueous products caused by microorganisms. They are highly effective microbicides (as used herein, "microbicides" includes bactericides, fungicides and algicides, and microbicidal activity is intended to include both the elimination of and the inhibition or prevention of growth of microbial organisms such as bacteria, fungi and algae). By suitable choice of functional groups, they are useful in a broad range of applications.
One significant area of application for isothiazolones is as microbicides in metal working fluids. Metal working fluids are proprietary combinations of chemicals, which may contain, inter alia, ingredients such as alkanolamines, pertroleum sulfonate surfactants, oils (napthenic, paraffinic, etc), chlorinated paraffins and fatty esters, sulfurized fatty compounds, phosphate esters, fatty acids and their amine salts, glycols, polglycols, boric acid esters and amides. They are utilized in the milling, machining, drilling, and other processing technologies for fabricating metal for the purposes of lubricating, cooling, preventing surface corrosion, and the like. They are sold in the form of active metal working fluid (MWF) concentrates, and are diluted in use to 1-10% active ingredients in water.
Because metal working fluids are recycled and stored, the growth of micro-organisms is favoured. Isothiazolones have been found effective in preventing the growth of such organisms. However, certain components in the metal working fluids tend to destroy the isothiazolone and so remove its microbicidal protective activity. This is a particular problem when the MWFs are in concentrate form. It has been found that even some other microbicides, present in combination with isothiazolones, may attack the isothiazolones. An example of this is the sodium salt of mescapto pyridine-N-oxide (sodium omadine), which has been found to remove 5-chloro-2-methyl isothiazolone from any system in which the two are present together.
Indeed, generally, it has long been recognized that either in storage prior to addition to a substrate to be treated or after addition, the efficacy of isothiazolones in many environments may be decreased because they are not stable under practical conditions of long term storage. Means have thus been sought for some time to improve the stability of isothiazolones.
U.S. Pat. Nos. 3,870,795 and 4,067,878 teach the stabilization of isothiazolones against chemical decomposition by addition of a metal nitrite or metal nitrate, but teach that other common metal salts, including carbonates, sulfates, chlorates, perchlorates, and chlorides are ineffective in stabilizing solutions of isothiazolones, such solutions usually being in water or in an hydroxylic solvent. U.S. Pat. Nos. 4,150,026 and 4,241,214 teach that metal salt complexes of isothiazolones are useful because they have enhanced thermal stability, while retaining biological activity.
It is known to use certain organic stabilizers for isothiazolones, generally for use situations where metal salts may create problems, such as corrosion, coagulation of latices, insolubility in non-aqueous media, interaction with the substrate to be stabilized, and the like. Formaldehyde or formaldehyde-releasing chemicals are known as stabilizers, (see U.S. Pat. Nos. 4,165,318 and 4,129,448), as are certain organic chemicals such as orthoesters (EP-A-315,464), epoxides (EP-A-342,852), and carbonyl compounds (copending European Application No. 90312417.0).